1. Field of the Invention
The present invention relates generally to the fields of lipid/liposome technology and DNA delivery. More specifically, the present invention relates to a stabilization of lipid:DNA formulations during nebulization.
2. Description of the Related Art
The development of liposomal formulations compatible with aerosol delivery has allowed the jet nebulizer to deliver nucleic acids preparations whose biological activity is maintained sufficient for therapeutic use. Utilization of liposomes for aerosol delivery has many advantages, including aqueous compatibility; sustained pulmonary release allowing maintanence therapeutic drug levels; and, further, liposomes facilitate intra-cellular delivery, particularly to respiratory epithelial cells.
The efficacy of localized, topical therapy via aerosols is determined by the amount of drug delivered at the sites of disease within the lung; and there are several different key parameters that determine the amount of delivery which interact to provide the therapeutic efficacy of aerosol formulations. For example, nebulizer design, flow rate, flow volume, particle size, hygroscopicity and the presence of ancillary equipment (tubing, connectors, mouth pieces, face masks, and the like), are important variables. Thus, aerosol output efficiency of appropriate particle sizes can be increased through proper implementation of the proper nebulizer device. Inappropriate implementation of the device and/or imperfect parameters can affect inhaled dosages, delivery sites and influence the therapeutic outcome.
Drug formulation also is a critical factor regulating aerosol output efficiency and aerodynamic properties of drug-liposomes. It has been discovered that drug-liposome output efficiency can be increased through the utilization of liposomes formulated with low phase transition temperatures (see Waldrep et al., J. of Aerosol Med. 7:1994 (1994) and Waldrep et al., Int'l J. of Pharmaceutics 97:205-12 (1993)). An additional method to increase aerosol drug-liposome output is to increase the drug and phospholipid reservoir concentrations. Nebulization of some drug-liposome formulations at greater than 50 mg/ml results in clogging of the nebulizer jets; yet empty liposomal formulations up to 150 mg/ml have been successfully nebulized (see Thomas, et al., Chest 99:1268-70 (1991)). Further, the aerosol performance (output and particle size) is influenced in part by physiochemical properties such as viscosity and surface tension. Such variables affect the maximal drug-liposome concentrations compatible with aerosol delivery via the jet nebulizer.
A problem associated with the aerosol delivery of cationic lipid:plasmid DNA formulations for the purpose of targeted pulmonary gene therapy is that the process of nebulization leads to a marked decrease in the transfection efficiency of the formulations. This is a major reason for the relatively low in vivo gene transfer efficiency of aerosolized formulations. A rapid loss in activity is associated with a wide variety of jet nebulizers and lipid:DNA formulations.
The prior art is deficient in the lack of effective means of improving the stabilization of lipid:DNA formulations during nebulization. The present invention fulfills this longstanding need and desire in the art.